1. Field of the Invention
The present invention relates to a radio network using infrared rays, radio waves and the like as a radio communication medium and a method of establishing a time synchronization among a plurality of buses. More particularly, this invention relates to a radio network in which a time synchronization may be satisfactorily established among a plurality of buses by adjusting a time of other bus based on time information of one bus.
2. Description of the Related Art
Heretofore, an IEEE (Institute of Electrical and Electronics Engineers) 1394 bus receives a remarkable attention as a multimedia bus suitable for connecting home electronic devices such as digital video recorders or connecting these electronic devices to a computer.
This IEEE1394 bus has two kinds of data transfer functions of asynchronous transfer function and isochronous transfer function. According to the asynchronous transfer function, an asynchronous communication of data is carried out in a memory-mapped I/O system. On the other hand, according to the isochronous transfer function, data communication is carried out by using channel numbers previously-set on the transmission side and the reception side, and an isochronous communication is carried out at the unit of 125 microseconds.
It is proposed that a radio network comprises a plurality of the above-mentioned IEEE1394 buses, for example, connected over radio waves to thereby transmit and receive video data and audio data among respective buses. Each bus includes a time management node, which is generally referred to as a cycle master, to manage a time of each bus. A time of each bus is counted by using a clock signal having a certain degree of accuracy. However, since there exists a constant error among clock signals, when a time is continuously counted to some extent, it is unavoidable that a time difference among respective buses is shifted. As described above, when video data and audio data are transmitted and received among respective buses, a displacement of a time difference among the respective buses exerts a bad influence upon reproduced pictures and sounds as a jitter component.
It is an object of the present invention to provide a radio network in which a time synchronization may be satisfactorily established among a plurality of buses.
A radio network according to the present invention is a radio network comprising a plurality of buses connected over radio waves and which includes means for adjusting a time of other bus by using time information of one bus.
The radio network according to the present invention, for example, includes a radio communication unit for effecting a radio communication among a plurality of buses. This radio communication unit comprises one control node and more than one controlled nodes controlled by this control node and wherein the control node is connected to one bus and the controlled node is connected to other bus.
The control node transmits time information from a time management node on a bus connected thereto to the controlled node. Then, the controlled node generates control information for adjusting a time by using time information transmitted from the control node and time information from a time management node on a bus connected thereto, and transmits such control information to a time management node on a bus connected thereto, whereby a time synchronization of buses to which the control node and the controlled node are connected may be established.
Also, the radio network according to the present invention, for example, includes a radio communication unit for effecting a radio communication among a plurality of buses. This radio communication unit comprises one control node and more than one controlled nodes controlled by this control node and wherein a controlled node is connected to one bus and a control node and a controlled node are connected to other buses.
The control node transmits time information from a time management node on a bus connected thereto to a controlled node. The controlled node connected to a bus other than one bus generates control information for adjusting a time by using time information transmitted from a control node and time information from a time management node on a bus connected thereto, and transmits such control information to a time management node on a bus connected thereto.
The controlled node connected to one bus generates control information by using time information transmitted from a control node and time information from a time management node on a bus connected thereto, and transmits such control information to a control node. Then, the control node receives control information transmitted from a controlled node connected to one bus, and transmits such control information to a time management node on a bus connected thereto, whereby a time synchronization of buses to which the control node and the controlled node are connected may be established.